Boris Johnson has said he is backing David Cameron in response to former media adviser Andy Coulson's claim he wanted to be Prime Minister.
Former Downing Street media adviser Andy Coulson reignited speculation by claiming the London Mayor was desperate to be prime minister but would rather see Mr Cameron "fail miserably" and take his place than stab him in the back.
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The talks descended into crisis on Friday when Canada's trade minister Chrystia Freeland walked out of meetings.
Police in New York are still investigating what the substance is and whether it could be harmful.
The Sherlock actor made the comment while he received an award for his humanitarian work.